There are two networks (a key sharing network, an application network) for a key generation/sharing system. The key sharing network is configured from a plurality of nodes that are interconnected by a plurality of links into a network. Each node includes a function of generating and sharing a random number with a correspondent node connected by a link, and a function of performing encrypted communication over the link by using the random number that is generated and shared as an encryption key (hereinafter, a link key). Also, some of the nodes include a function of generating an encryption key (hereinafter, an application key) which is a random number independently of the link, and a function of transmitting the application key to another node over a link.
An application includes a function of acquiring an application key from a node, and performing encrypted data communication with another application by using the acquired application key as an encryption key. The encrypted data communication here may be realized by a network (an application network) different from the key sharing network, such as the Internet. Also, the node and the application may be realized in an integrated manner. The node and the application may also be configured as independent terminals, and the application key may be transmitted/received between the two.
The function of the node of generating and sharing a random number (a link key) with a correspondent node connected by a link may also be realized by a technique generally called quantum cryptography or quantum key distribution (QKD), for example.
In the key generation/sharing system, one of the most important resources is the key. Accordingly, with a node connected with a plurality of applications, the method of assigning an application key to each application (a key assignment method) is important. For example, a situation where key assignment that satisfies the volume requested by an application (key request rate) fails during system operation has to be handled appropriately.